China’s National Medical Products Administration has approved a new therapy for patients with mild to moderate Alzheimer’s disease – a seaweed extract thought to alter the gut microbiome profile and subsequently decrease microbiome-driven neuroinflammation.
Dr. Paul Aisen
Sodium oligomannate – dubbed GV-971 – won approval based on a 36-week, placebo-controlled, phase 3 study of 818 patients with mild to moderate Alzheimer’s disease (AD). The study hit its primary endpoint of change on the Alzheimer’s Disease Assessment Scale cognitive portion (ADAS-cog12). It did not meet any of the trial’s other cognitive or functional secondary endpoints.
A portion of the data were presented last year at the Clinical Trials on Alzheimer’s Disease meeting in Barcelona. But the full study has never appeared in a peer-reviewed journal. A truncated version is publicly available on the website of Shanghai Green Valley Pharmaceuticals, the company developing the molecule.
Shanghai Green Valley contends that it reduces neuroinflammation by improving a proinflammatory microbiome profile that it says is characteristic of AD. However, the mechanism by which GV-971 alters intestinal bacterial composition is unclear – or at least it is not fully described in the public literature.
In the United States, some key researchers appraised the news with a cautiously optimistic eye, while others pointed noted that the AD-microbiome link is an unproven concept, and that it was evaluated in a study of questionable worth.
“The company has presented data that suggest there is a modest cognitive benefit to this treatment,” Paul S. Aisen, MD, said in an interview. “The key secondary endpoint was missed, and the other secondary endpoints showed no benefit. It’s a single trial and the mechanism is still unclear.”
“We do need to pursue all possible leads, and I’m glad the company is pursuing additional studies, but I wouldn’t draw a firm conclusion from these data. And they certainly would not be enough to win approval in the U.S.,” said Dr. Aisen, founding director Alzheimer’s Therapeutic Research Institute at the University of Southern California, Los Angeles.
Preclinical findings on GV-971
In commenting on preclinical findings of GV-971 published in Cell Research in September 2019, David Holtzman, MD, associate director of the Alzheimer’s disease research center at Washington University, St. Louis, and coauthors observed that the data support research exploring treatments that modulate the gut microbiome but leave it unclear as to whether GV-971 has AD-specific effects.
“[The company shows] that GV-971 decreases amyloid beta-related pathologies by reconditioning the gut microbiota, providing further evidence that gut-targeted interventions may serve as novel strategies to tackle AD,” Dr. Holtzman and coauthors wrote. “Whether this potential mechanism represents an AD-specific process is not clear, since there is great overlap in immunological changes and gut dysbiosis with other diseases. … In addition, although this study reveals that gut reconditioning may be one mechanism of action of the drug GV-971, it does not rule out other possible mechanisms. For example, GV-971 may attenuate AD pathogenesis by directly inhibiting neuroinflammation or amyloid-beta fibril formation. However, there is no question that [these] data further [support] the emerging idea that modulation of the gut microbiome via treatments such as GV-971 or other strategies should be further explored as novel strategies to slow the progression of AD.”
Sodium oligomannate is a long-chain saccharide extracted from brown sea algae and consists of acidic linear oligosaccharides with structures ranging from dimers to decamers. Related molecules without the sugar backbone were inactive, suggesting that the saccharides are the active portion, Xinyi Wang of Shanghai Green Valley and colleagues wrote in the Cell Research paper.
Based on these studies, the company contends that Alzheimer’s progression is accompanied by a characteristic microbiome change to a proinflammatory profile. And indeed, two transgenic Alzheimer’s mouse models – one with five familial AD mutations (5xFAD) and one with mutations of amyloid precursor protein and presenilin 1 (APP/PS1) – showed similar gradual age- and progression-related decreases of Bacteroides and Verrucomicrobia, two components of a normal microbiome. Bacteroides species perform key functions necessary for survival, including sensing and adapting to nutrient variability, expelling toxins, and stimulating the immune system). Species of the Verrucomicrobia phylum are important in glucose homeostasis. The decline in Bacteroides and Verrucomicrobia species is accompanied by an increase in concomitant proinflammatory species.
The investigators then explored the relationship between the microbiome composition and cognitive function in both transgenic models and a wild-type mouse.
First, they showed that the bacterial populations shifted as the mice aged and their AD pathology developed. This was accompanied by an uptick in activated microglia and, in turn, proinflammatory T1 helper cells that migrated through the intestinal membranes and into the periphery, then cross the blood-brain barrier to enter the brain.
Then the investigators used a cocktail of powerful antibiotics to disturb the intestinal flora in both transgenic and wild-type mice. After this, the 5xFAD mice showed fewer activated microglia and fewer infiltrating T cells. Later, they gave wild-type mice a fecal transplant from the 5xFAD mice. The wild-type mice developed more activated and infiltrating cells and their microbiome began to resemble that of the transgenic mice. Conversely, when the transgenic mice received a transplant from the wild-type mice, their microbiome changed to resemble the donors’, and their activated and infiltrating cells declined.
After this, the team gave GV-971 to the mice. The APP/PS1 mice improved cognitively, and the 5xFAD mice had fewer activated and infiltrating cells, fewer amyloid brain plaques, and less tau phosphorylation. These changes were accompanied by higher levels of two amino acids, phenylalanine and isoleucine. These proteins appear to act on T-cell proliferation and differentiation, they said.
“Taken together, these analyses suggest the idea that gut dysbiosis contributes to [phenylalanine and isoleucine] elevation, which drives the proliferation/differentiation and brain infiltration of [T1 helper] cells,” Dr. Holtzman and coauthors wrote. “These infiltrating Th1 cells may then further activate microglia and contribute to amyloid-related pathogenesis.”